I think my sub box needs more bracing

[TLS Guy]

I'm concerned about the creaking you describe. I fear that may be coming from butt joints. At least that is what the pictures show.

I'm always telling people not to use butt joints in speaker building. You need to use dado joints, use good carpenters glue and clamp very tight as it set up. Do not use screws or fasteners, they can creak as well.

The pressures inside speaker enclosures are enormous! On large panels that translates into lots of thrust, which is pressure X area of a panel.

When you build your next speaker use figure of 8 type bracing and rout the side panels to take the brace panels.

 

[MrBoat]

Is why I suggested plywood for the brace. It's exponentially stronger than a brace made of MDF, which has next to no directional advantage when stood on edge until it becomes a lot larger, beyond what it adds with mass. Plywood, supported by the front and rear panels which arrive at the foundation of the bottom of the cabinet is much stronger and you will get no sagging of the top panel over time.

By all means, if you want to add a cross brace, half notch it with the longitudinal brace or make a grid. This is much like the stringer systems in boats. You could use any combination of grids depending on the expanse of the cabinet.

 

[MrBoat]

Some of these cabinet designs for subs, it always seems to me that they are pushing the limits with the density of 3/4" MDF. I imagine some of these manufactured subs are using 1" material for the cabinets. It just seems with most larger speakers using double thickness for the baffles, the next logical step down for the sides would be 1" thick. Going from double thickness to half, just seems kind of extreme.

 

[yonyz]

Well it was my first ever build and I didn't know any better. I was told that the bracing would be sufficient.

Anyhow, yes, those are butt joints and the carpenter used glue and nails. I don't think clamps were used.

So, MrBoat and TLS Guy, would you suggest dowels to connect the top panel to the bottom, or a horizontal strip that connects the top panel to the side, front and back panels?

 

[MrBoat]

Well it was my first ever build and I didn't know any better. I was told that the bracing would be sufficient.

Anyhow, yes, those are butt joints and the carpenter used glue and nails. I don't think clamps were used.

So, MrBoat and TLS Guy, would you suggest dowels to connect the top panel to the bottom, or a horizontal strip that connects the top panel to the side, front and back panels?

The one front to back would stiffen it up significantly. One front to back and another side to side, more so. Try one first, and if it still seems wimpy, add another.

Adding a dowel top to bottom would be less effective just resting on that port shelf without adding a shim between that port shelf and the bottom where the dowel would be located.

It's ok if it's your first build. Nobody is blaming this on that fact. You're asking the right questions and you did seem to notice the problem so that's good.

The brace I suggest will only be really effective if it's plywood though.

 

[MrBoat]

Either one front to rear, or two side to side that divides the top panel into thirds. Could possibly use taller braces in that direction.

ETA: I'm going to maintain the idea of the front to rear treatment. Reason being, trying to turn an exact length side to side brace in there is going to be difficult. It will get longer than the space before it turns all the way and possibly loosen one of the butt joints.

If you don't have plywood, a 1x2 of solid lumber would be 2nd choice. I would turn the cabinet upside down, glue up the beam, install it, and use props on the inside of the cabinet to press the beam in securely until the glue dries.

 

[yonyz]

All I have is a piece of plywood with formica on it. I was told I cannot glue it because of that.
I'll have to pay a carpenter to cut me some pieces of "bare" plywood. While I'm at it, is there a way to strengthen the joints?

 

[MrBoat]

I find it hard to believe the joints need any strengthening if a carpenter put it together. Wood glue is like carpentry 101. Doesn't matter if your plywood has formica on it because you are gluing only the edge, not the face. The same dimension that is glued on your window brace. The squeaking could be from a loose driver or plate amp too. Is there a gasket on the driver and the plate amp where they contact the cabinet?

I'd just go up to a home center and buy a 'straight' piece of 1x2 for a couple bucks. You would want to glue the 1" (actually it's 3/4" x 1.5") dimension. Or maybe one of the handy panels at the home center is big enough and you could get them to cut it for you.

 

[yonyz]

I find it hard to believe the joints need any strengthening if a carpenter put it together. Wood glue is like carpentry 101. Doesn't matter if your plywood has formica on it because you are gluing only the edge, not the face. The same dimension that is glued on your window brace. The squeaking could be from a loose driver or plate amp too. Is there a gasket on the driver and the plate amp where they contact the cabinet?

I'd just go up to a home center and buy a 'straight' piece of 1x2 for a couple bucks. You would want to glue the 1" (actually it's 3/4" x 1.5") dimension. Or maybe one of the handy panels at the home center is big enough and you could get them to cut it for you.

I need to glue the top of the plywood piece to the top panel, so the formica will interfere.
Our home center shops don't cut boards. I'll have to go directly to a carpenter or something like that.

 

[MrBoat]

Just so we're clear what I am talking about, this is a plywood stiffener made from 18mm plywood. It would be installed to the panel as shown. This stiffener is approx. 18mm X 50mm X whatever length needed. There are two of these supporting the router table underneath where the screws are. This will guarantee that the top remains stable and flat and will not sag over time.

 

[yonyz]

OK, here's a little sketch:

The width of the material is 6cm for all pieces. The thickness could be either 18mm or 36mm (if I stack two pieces on top of each other).

It's made of 6 pieces that I'll glue inside the cabinet.

Does this look good?

By the way, how should I remove the driver?

 

[rojo]

Hey @yonyz I must apologize for the advice that your designed level of bracing was sufficient. My own sub box has less bracing than yours with a stronger driver than yours, and has none of the creaking issues you described. I'm with TLS Guy, suspecting the problem is with insufficiently sealed joints. I think adding bracing is certainly not a bad idea, and I'm not going to argue with @MrBoat or the other experienced builders here. But I also wonder whether adding some sort of expanding glue or caulk to all seams within the box would have any additional positive effect. In any case, again, I'm truly sorry for offering crappy advice and creating additional work for you.

 

[yonyz]

Hey @yonyz I must apologize for the advice that your designed level of bracing was sufficient. My own sub box has less bracing than yours with a stronger driver than yours, and has none of the creaking issues you described. I'm with TLS Guy, suspecting the problem is with insufficiently sealed joints. I think adding bracing is certainly not a bad idea, and I'm not going to argue with @MrBoat or the other experienced builders here. But I also wonder whether adding some sort of expanding glue or caulk to all seams within the box would have any additional positive effect. In any case, again, I'm truly sorry for offering crappy advice and creating additional work for you.

Oh it's OK, you're not the only one who thought that the bracing would be sufficient.
I've added silicone to the inside to make it better sealed after I painted it, but I think it dose nothing to affect the strength of the "structure", because it's just silicone.

I'll add the bracing and we'll see how it goes.

Any advice as to how to remove the driver (short of kicking its magnet through the plate amp hole) would be appreciated.

I look at this in a positive way, by the way. This is a small fix that will make this great sub even better. I can't thank you enough, this sub has been such a huge upgrade to my home theater experience.

 

[MrBoat]

OK, here's a little sketch:

The width of the material is 6cm for all pieces. The thickness could be either 18mm or 36mm (if I stack two pieces on top of each other).

It's made of 6 pieces that I'll glue inside the cabinet.

Does this look good?

By the way, how should I remove the driver?

Pieces of what? All that does is add a little mass and not much in the way of rigidity. Better than nothing, I suppose, but not much. Plywood, on edge like the photo I posted is exponentially stronger. Plywood in the flat orientation is flexible. On edge, it is rigid. And what is with the joint in the middle of that grid? That defeats the purpose even further.

Perhaps it will help and be just enough.

 

[yonyz]

Pieces of what? All that does is add a little mass and not much in the way of rigidity. Better than nothing, I suppose, but not much. Plywood, on edge like the photo I posted is exponentially stronger. Plywood in the flat orientation is flexible. On edge, it is rigid. And what is with the joint in the middle of that grid? That defeats the purpose even further.

Perhaps it will help and be just enough.

Pieces of plywood, of course.
If I put it on its edge, what should be its width? 6cm will definitely not fit if it's on its edge.

The joint in the middle is necessary because I most likely won't be able to maneuver a full-length piece inside the box. Or maybe I will... I don't know.

 

[MrBoat]

Pieces of plywood, of course.
If I put it on its edge, what should be its width? 6cm will definitely not fit if it's on its edge.

The joint in the middle is necessary because I most likely won't be able to maneuver a full-length piece inside the box. Or maybe I will... I don't know.

4.5 + cm would be plenty tall enough. If you take the driver, or the plate amp out, and it is cut exactly the length front to rear, it will fit as long as you install it evenly. If you have enough plywood, make two and double them up, or space them apart evenly. You're just trying to subdue vibration or flexure in the panel. This will significantly stiffen that top panel.


Doubled as such. These are approx. 5cm tall. Together they are roughly 5cm X 36mm.

 

[MrBoat]

Don't laugh at my lack of computer drawing. This shows roughly where and how this needs to go.

I am assuming the top panel is arranged the same as the bottom in your sketch.

 

[yonyz]

Your assumption is correct, and that's indeed where I meant for the support piece to go.

Unfortunately, there's no room for a 4.5cm tall piece, but only 2cm or so, because of the location of the plate amp. Will this work? As mentioned before, I can add pieces that connect the sides as well.

 

[j_garcia]

Yes, I'd think that will work fine.

 

[MrBoat]

That should help. If it's not enough, you can always add the taller brace to that just past the reach of the plate amp since your grid will help carry it through.

The original picture was misleading with the space that is left above the amp opening.